Stents are generally designed as tubular support structures that can be used in a variety of medical procedures to treat blockages, occlusions, narrowing ailments and other problems that restrict flow through body vessels. Expandable stents are radially compressed for delivery within a vessel and then radially expanded once in place at a treatment site, where the tubular support structure of the stent contacts and supports the inner wall of the vessel. Expandable stents are generally classified as either balloon-expandable or self-expanding. Balloon-expandable stents expand in response to the inflation of a balloon, while self-expanding stents expand spontaneously when released from a delivery device.
Generally, to deliver a self-expanding stent or other intraluminal device into a vessel of interest, a hollow needle is used to penetrate the vessel and a wire guide is threaded through the needle and into the vessel. The needle is removed, and an introduction catheter is inserted over the wire guide. The stent is radially compressed to a low profile configuration and inserted into a tubular retaining sheath that prevents the stent from expanding during delivery. The stent and the sheath are directed through the introduction catheter and into the vessel. Once the stent reaches the treatment site, the sheath is retracted and the stent expands from its low profile configuration to an expanded state in which it exerts an outward radial force against the vessel wall.
During retraction of the sheath, the distal end of the stent typically expands first while the proximal end remains restrained by a distal portion of the sheath. Continued retraction of the sheath allows the remainder of the stent to be gradually released from the sheath. A problem may arise, however, due to friction between the inner wall of the sheath and the surface of the stent. Instead of sliding smoothly over the stent, the sheath may tend to grip the stent as it retracts, causing the stent to stretch, twist, or otherwise deform. Since the distal end of the stent is normally in contact with the vessel wall during the retraction, this deformation may in turn be transferred to the vessel. Axial elongation or twisting of the stent structure may also lead to inaccurate placement of the stent at the treatment site.
Accordingly, it is apparent to the inventors that an improved deployment system for an expandable stent would be advantageous.